The present invention relates generally to an improved local oxidation of silicon (LOCOS) process. More specifically, improved LOCOS and silicon etch processes are disclosed that provide an effective isolation permitting device scaling beyond the present state of the art.
Isolation is a fundamental semiconductor device fabrication process designed to electrically isolate active regions in a semiconductor substrate. The incorporated US patent referenced above identifies a number of conventional isolation methods, and describes some of the drawbacks to implementation of these various processes. Conventional LOCOS, or modified LOCOS, remains the preferred process for high-volume manufacturing when implementing standard sub-micron integrated circuit technology.
Research on improved processes has heretofore resulted in increasingly complex processing requirement, while continuing to produce various device degradations due to various defects. It is important to design a simple, cost effective alternative to LOCOS processing to overcome some or all of its disadvantages. The well-known disadvantages of conventional LOCOS processing are that the resulting isolation oxide is not planar, nor is it deep enough in the substrate to provide effective isolation to improve device scaling without compromising device performance.
Scaling refers to an ability to improve transistor density in a semiconductor by decreasing an amount of substrate area required to implement various semiconductor structures in the substrate. The LOCOS process does not scale well in that variations in processing to reduce the substrate area required to form the isolation regions negatively impacts on the performance of devices formed in the active regions.
From the foregoing, it is apparent that an improved process for forming isolation regions in a semiconductor substrate is desirable. This improved process should offer the advantages of conventional LOCOS (i.e., it is simple to implement and has few stresses/defects that adversely affect device performance) and improves on some of its disadvantages (e.g., planarity, scalability, bird's beak formation, and isolation effectiveness).